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Heidenhain: Tool Measurement (DA 301 TL)
Touch probes for machine tools
HEIDENHAIN has been developing and manufacturing touch probes for workpiece and tool measurement on machine tools for over 30 years now, in particular for milling machines and machining centers. The setup, measuring and monitoring functions of the touch probes can be fully automated—in conjunction with most NC controls they can even be controlled by the program—and help to reduce costs. TS triggering touch probes handle the measurement of workpieces, while TT touch probes and TL laser systems are available for the measurement of tools.
Touch probes from HEIDENHAIN have a whole series of technologically convincing features, such as the contact-free optical sensors, the integrated blower/flusher jets for cleaning the measuring point, or the large deflection path with a rated break point in the stylus. Some milestones of these products’ technology include the SE 540, which was the first transceiver unit for full integration in the spindle housing; the TS 444, which was the first touch probe without a battery; and the TS 460 with its additional collision protection.
Effective collision protection
A mechanical adapter on the TS 460 between the touch probe and the taper shank provides additional collision protection by also protecting the touch probe’s housing. In the event of a light collision against a fixture or workpiece, the touch probe can absorb the shock. At the same time, an integrated switch deactivates the ready signal and the control stops the machine. This way an incorrect tilting movement does not lead to serious damage. The collision protection of the TS 460 compensates smaller collisions, and prevents greater damage to the spindle or other parts of the machine.
Signal transmission via radio or infrared signals
The combined signal transmission in the TS 460 and TT 460 touch probes brings together the advantages of infrared and wireless transmission into one system. Infrared transmission is ideal for compact machines with an enclosed work envelope, whereas wireless transmission is mainly used on large machine tools.
Tool measurement on the machine shortens non-productive times, increases machining accuracy and reduces scrapping and reworking of machined parts. With the tactile TT touch probes and the contact-free TL laser systems, HEIDENHAIN offers two completely different possibilities for tool measurement.Probing
The TL laser systems operate as high precision light barriers without any contact. A laser light source (protection class 2 as per IEC 825) emits a laser beam. The opposing receiver unit detects the laser beam and so captures every interruption. For any change in status—such as when a tool interrupts the laser beam or is removed again—the integral electronics generate a trigger pulse for a defined duration. This dynamic signal DYN is transmitted to the NC control, where it is used for capturing the position value. In addition, the laser system outputs the static signal STA for the duration that the laser beam is interrupted.
Calibrating
Before measurement with the TL laser system can be started, the system must be calibrated, meaning that the exact position of the trigger points relative to the machine coordinate system must be determined. A reference tool, available as an accessory, is used for this purpose. It has a characteristic shape for calibration, with a cylindrical dowel pin and a stepped inspection diameter for measurement in the positive and negative Z axis directions (for determining the exact position of the center of the laser beam in Z). The reference tool is clamped into the tool holder, and its length, diameter and height are measured very exactly. A cylindrical dowel pin can suffice for simple applications. The best possible runout is to be ensured for the calibration measurement.
Probing Strategies
The selection of the probing strategy also influences the reliability of the measurement. The measured value can be captured either when the tool is moved into the laser beam (“pushing measurement”) or when it is removed (“pulling measurement”). The pulling measurement ensures a high degree of protection against the influence of coolant and swarf, while the pushing measurement is the better method for engraving bits and tools with very small shaft diameters.